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 Forum index » Instruments and Equipment » Alesis Andromeda
Testing The OSC's and filters
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nil



Joined: Jan 27, 2006
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PostPosted: Sat Feb 04, 2006 11:22 am    Post subject: Testing The OSC's and filters Reply with quote  Mark this post and the followings unread

I am buying a used Andromeda. I wanted to know what to test for when i get the unit so here are a couple questions.

1. Do i test each oscillator and see if it is in the range of +/- 4 cents?

2. Why do i have to test the filters/vca? How do i actually test this? (I read sunny's post ,but it was really confusing and i dont know what he was trying to say in there).

3. Is there anything else i should test for when i get this unit?
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mosc
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PostPosted: Sat Feb 04, 2006 3:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

see this topic for Sunny's post http://electro-music.com/forum/topic-9791.html
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nil



Joined: Jan 27, 2006
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Location: USA

PostPosted: Sun Feb 05, 2006 1:27 am    Post subject: Re: Testing The OSC's and filters Reply with quote  Mark this post and the followings unread

nil wrote:
I am buying a used Andromeda. I wanted to know what to test for when i get the unit so here are a couple questions.

1. Do i test each oscillator and see if it is in the range of +/- 4 cents?

2. Why do i have to test the filters/vca? How do i actually test this? (I read sunny's post ,but it was really confusing and i dont know what he was trying to say in there).

3. Is there anything else i should test for when i get this unit?



Questions 2 and 3 still weren't answered
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ian-s



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PostPosted: Sun Feb 05, 2006 1:44 am    Post subject: Re: Testing The OSC's and filters Reply with quote  Mark this post and the followings unread

nil wrote:
Questions 2 and 3 still weren't answered


Shocked

2.
Sounds to me Sunny is warning that there are dodgy chips in some of these units, so it may test fine pre-purchase but become unusable after a short time (and require expensive repairs).

3.
Just play the thing, try as many presets as you can, if your happy with the sound and are not put off by its 'software plugin' looks or potential maintenance issues, buy it.
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nil



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PostPosted: Sun Feb 05, 2006 2:54 am    Post subject: Reply with quote  Mark this post and the followings unread

How can filters go bad?

If a filter goes bad can i hear it?

Also is there tunings for filters? If so do i have to make sure these tune as well?
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paul e.



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PostPosted: Sun Feb 05, 2006 8:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

always check the best-before-date of filters....
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ian-s



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PostPosted: Sun Feb 05, 2006 10:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

paul e. wrote:
always check the best-before-date of filters....


Laughing

Analog filters can self oscillate at high resonance settings, producing a sine wave. So they should be able to track the keyboard. Probably dont require the same range and accuracy as a VCO though.

Unless it is oscillating, variations in the filters will just mean that some notes sound different to others, like softer, brighter etc. This is part of the charm of real analog but in the worst case, it can make the machine unplayable.
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nickelodeus



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PostPosted: Tue Feb 07, 2006 4:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ahh I always wondered what the self-oscillating filters meant. A couple of additional questions....
1) is this ability ever useful....ie used in the world of synth programming to produce a certain charactaristic?

2) How do i get my a6 to do this to hear the effect ?

thanks
nic
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Blue Hell
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PostPosted: Tue Feb 07, 2006 5:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

nickelodeus wrote:

1) is this ability ever useful....ie used in the world of synth programming to produce a certain charactaristic?

As an extra oscillator, or some say it makes a better sine wave than their main osc.
Quote:

2) How do i get my a6 to do this to hear the effect ?

By turningup the filter Q until it resonates. Got no details for the synth in question, but on a digital filter some very low level noise may be needed at the filter input in order to give the filter something to resonate on.
[/quote]

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Tim Kleinert



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PostPosted: Wed Feb 08, 2006 2:39 am    Post subject: Reply with quote  Mark this post and the followings unread

When the unit is well warmed up and tuned, the Andros filters track the keyboard perfectly over the entire range. (Well done, Alesis!)

Oscillators generate a sine wave output by using the triangle output with some additional waveshaping. Hence it is never 100% pure. For a 100% pure sine wave (given that the signal path isn't clipping), self-oscillating filters are used with preference.

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nickelodeus



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PostPosted: Thu Feb 09, 2006 4:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey Guys....thankyou for your responses!

You'll have to forgive me but I'm trying to learn more about synthesis so I can start making my own sounds from nothing ...not just altering existing patches!!

Is it ok to ask a couple more questions? .....sorry if this is basic stuff Embarassed

1) I am right in thinking that filter Q is the same as resonance?

2) If I were to get the filter to self oscillate....do I keep the cutoff low or high? Also, if I used the filter as an oscillator could i then use the oscillator to do something interesting to the sound?

3)What does it mean when ou say that the filters track the keyboard perfectly on the a6?


Thanks guys
nic
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mosc
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PostPosted: Thu Feb 09, 2006 7:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Q is the same as resonance.

When we say the something tracks the keyboard it means that the pitches of the modules follow the pitches on the keyboard. Essentially, this means the instrument plays in tune.

When you crank up the resonance and the filter starts oscillating, then the cutoff works like the frequency knob on an oscillator. Cutoff should really be "cutoff frequency".

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ian-s



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PostPosted: Thu Feb 09, 2006 10:51 am    Post subject: Reply with quote  Mark this post and the followings unread

nickelodeus wrote:
Also, if I used the filter as an oscillator could i then use the oscillator to do something interesting to the sound?


You would probably be able to modulate the filter frequency with one or both the oscillators, giving bell/metallic type sounds. The filter ADSR is also available to bend these sounds.

Careful adjustment of the resonance around the onset of oscillation, can give interesting effects as the filter and oscillator frequencies interact.
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nil



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PostPosted: Fri Feb 10, 2006 6:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just got my andromeda...i really like this thing..it was off of ebay so im just making sure it's in good shape....


i tuned it and was cheking tuning....it's never exactly the note i play it fluctuates...........how much should it fluctuate by?


i think sunny said +-4 cents...would this be correct?
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mosc
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PostPosted: Fri Feb 10, 2006 9:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Might be best to send Sunny a PM if someone who actually owns an A6 doesn't answer.

Congrats on the new synth. I hope you enjoy it. I think they are great instruments.

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Blue Hell
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PostPosted: Sat Feb 11, 2006 6:18 am    Post subject: Reply with quote  Mark this post and the followings unread

nil wrote:
...it's never exactly the note i play it fluctuates


Just in case: be sure to have all frequency modulation on oscillators off.
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sunny pedaal



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PostPosted: Sat Feb 11, 2006 7:45 am    Post subject: Reply with quote  Mark this post and the followings unread

nil wrote:



i think sunny said +-4 cents...would this be correct?


yes,
make sure you warmed her up sufficiently ( 15 minutes should do ) to make life easier keep temptuning and maybe also background tuning on. take the default patch and keep the modwheel off and also switch of the oscilator and filter modulations. try testing b.e. first only osc1 and thereafter all osc's 2( voice assign to rotate and watch the voices playing under global-> vox monitor)

now +-4cent should be reasonable for this analog synth . when some voices are too much out of tune you might try it again after tuning that seperate voice only by when in vox monitor mode switching off the other voices and then pressing osc freq tune ( under tune).
more than 4 cents deviation start becoming annoying as they cause too audible beatings, some slow drifting ( about or less than 4cents) is ( on this synth) inherent to analog i guess and makes it even more lifely.
afcourse your tuner should be good enough to detect the difference , mostly they are accurate within +-1cent , some older guitar tuners however only within +-3cents, (very good ones go up to 1/100 cent), you have to watch for that in the specs of your tuner and afcourse add it to the acceptable deviation of +-4cents.
also check the filters once, the same procedure exept that you'll switch off the oscilars and with filter two turn up the resonance fully, with a keytracking of 50. tune the middle A and thereafter measure it over the keyboard. however most known problems occur due to improper osc chips. when filters break down mostly it can easily be heard because of some clear distortion b.e.
congratualations with the synth when in good shape it's a cracker!
fr. gr. sunny
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bentropy



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PostPosted: Thu Oct 19, 2006 4:56 pm    Post subject:  Andromeda owner seeks help diagnosing issues
Subject description: possible defects on my new (used) andromeda?
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Hi,
I just got a used Andromeda off of Ebay, from a seller who is only giving me 3 days to return it if something is wrong. I didn't realize these things were so temperamental and inconsistent in quality, or I wouldn't have bid.
So now I'm trying to perform diagnostics.

I don't have a tuner handy now, but here's what I've done:
I've tried to follow Sunny's guidelines, posted on Sat Feb 11, 2006 2:45 pm
- performed an autotune after the machine has warmed up,
- turned off all the LFOs and modulators I think might affect pitch, that I know how to,
- with both oscillators on, played a single note, in slow overlapping repetition.

What I hear worries me: on some notes, the two oscillators play in quite close unison, but on almost every other note I hit and hold, I hear beating from tuning differences between them, esp noticible in upper octaves. Is this indicative of the bad oscillator chips?

Sunny has referred to 'b.e.' What does this mean ? Before envelope?

Also, a separate issue is that the aftertouch seems strange to me. If I assign it to, say, an oscillator's pitch, and map a range for the values, there is a very narrow range of pressure to pass through the in-between values. Mostly it sounds binary, with an un-pressured state and a pressured one, rather than continuous depending on how hard I press.

I hope I'm not screwed. I think the seller would be difficult or impossible to send this back to and get my ~$1700.

hope I've been clear, thanks a lot,
Ben
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sunny pedaal



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PostPosted: Fri Oct 20, 2006 1:26 am    Post subject: Reply with quote  Mark this post and the followings unread

b.e. means "by example"
the aftertouch isn't the most super one , as long as it works on all keys , it should be oke, you can eventually tune it more to your likenings a bit later.
the beating of the oscillators could be more of a problem.
to find out this first remember that a slight bit of beating could be normal as long as:
the beating isn't too fast in frequency, once every few seconds ( once in five seconds is as good as they can get i guess) should be oke in the higher frequencies. a few times every second is too much.
you could , after warming up test every voice apart and monitor them by mon vox. then when you know which voices are best and which are worst retry tuning the oscillators with the good voices turned off. when they are in the normal range switch it of and proceed.
in the end they should all be in the "normal" range as described above, and thus all voices should have been turned off as they have passed the test.( this might take you at least 5 times or more passing the test)
if one or more voices can't be tuned within the normal range , if ba.e. one voices beatings really remains to keep happening a few times every second, you probably have a not so good chip for that voice and it should be switched off or replaced. ( this offcourse in not too extreme settings so put the osc to 440 hz and test over the 5 octaves, not transposing the keyboard).
the a6 is not perfect but it should be a reasonable enough analog synth.
after all for 1700$ you almost could also find another a6 when needed.
let us get a notice on the results you found so we might discussed them further.
fr.gr. sunny[/b]
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sunny pedaal



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PostPosted: Fri Oct 20, 2006 1:36 am    Post subject: Reply with quote  Mark this post and the followings unread

one thing more : after warming up and tuning it by autotune , might be an idea to "restore tuning tables"
do this by restarting while holding down softbutton ...., ?i thought number two under the screen , however have to find the manual again to find out exactly. if you have one manual yourself just look that one up and try it also before going on testing.
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